About Landau–Hopf scenario in a system of coupled self-oscillators

The conditions are discussed for which an ensemble of interacting oscillators may demonstrate the Landau–Hopf scenario of successive birth of multi-frequency quasi-periodic motions. A model is proposed that is a network of five globally coupled oscillators characterized by controlled degree of activation of individual oscillators. Illustrations are given for successive birth of tori of increasing dimension via quasi-periodic Hopf bifurcations.     

Irreversible Photoinduced Insulator-Metal Transition in Charge Ordered Pr 0.75 Na 0.25 MnO 3

Irreversible photoinduced insulator-metal transition has been observed in a perovskite manganite doped with monovalent Na + , Pr 0.75 Na 0.25 MnO 3 . The increase of the conductance is estimated to be of the order of 10 4 -10 5 , considering the shallow penetration depth ( ¨ 0.1 µm) of illumination light. Analysis of the dc- and ac-susceptibility data shows that the system is in a cluster glass state below 45 K, which means that ferromagnetic metallic clusters exist in insulating matrix. The photo-excitation helps the clusters to dislodge from a local energy minimum and to seek more stable configuration. The observed large increase of the conductivity can be well explained by the percolative conduction. We argue that metastability is due to the large charge mismatch between the monovalent Na + ion and trivalent Pr 3+ ion or the deviation of the average Mn valency from 3.5+.     

Synthesis and structure of complexes of phosphorus pentachloride with 4‐dimethylaminopyridine and n‐methylimidazole

Complexes of phosphorus pentachloride with 4‐dimethylaminopyridine and N‐methylimidazole were synthesized. The molecular structure of the phosphorus pentachloride complex with N‐methylimidazole was determined by single‐crystal X‐ray diffraction. In the cationic part of the complex, the phosphorus atom possesses four P Cl bonds within the range 2.109–2.148 Å and two cis‐P–N bonds (1.811 and 1.832 Å) with N‐methylimidazole and exhibits slightly distorted octahedral coordination with angles at phosphorus atom in the range 87.57°–91.50°. The relative stability of the cis and trans conformations of the complex was studied by DFT calculations. The chemical properties and reactivity of the compounds obtained are determined; their utility as condensing agents in the synthesis of amides from acids and amines was shown. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:171–177, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20392     

Nucleophilic catalysis of phosphorus trichloride oxygen oxidation

The effect of nucleophilic catalysis on phosphorus trichloride oxygen oxidation is discovered. A number of nucleophilic catalysts for the phosphorus trichloride oxidation are found. Triethylamine, 4‐dimethylaminopyridine (DMAP), and tetramethylurea are amongst them. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:408–411, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20439     

Crystal structure and luminescence properties of the barium europium tetragermanate Ba2Eu2Ge4O13

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Brennstoffe

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Diterpenes from the Brown Alga Dictyota crenulata

The crude extract of the Brazilian brown alga Dictyota crenulata was analyzed by NMR spectroscopy and HRGC-MS techniques. Seven diterpenes were identified: pachydictyol A, dictyodial, 4beta-hydroxydictyodial A, 4beta-acetoxydictyodial A, isopachydictyol A, dictyol C and dictyotadiol. Xeniane diterpenes have previously been found in D. crenulata from the Pacific Ocean. The results characterize D. crenulata as a species that provides prenylated guaiane (group I) and xeniane diterpenes (group III), thus making it a new source of potential antiviral products.     

Isotachophoretic determination of hydrosulfite and metabisulfite in technical samples

A method for determination of metabisulfite and hydrosulfite in poultice and decolorant by isotachophoresis was developed. Metabisulfite and hydrosulfite are ionizable oxoanions of sulfur of similar character that can easily be oxidized to sulfates. To protect the analytes from oxidation the solid samples were dissolved in a 1% (w/v) solution of formaldehyde. Hydrosulfite and metabisulfite present in the samples were transformed by the reaction with formaldehyde to stable compounds, hydroxymethanesulfinate and hydroxymethanesulfonate that were determined isotachophoretically without any pretreatment except for sample filtering and degassing. A capillary of 0.4 mm i.d. and 100 mm effective length made of fluorinated ethylene-propylene copolymer was filled with an electrolyte system consisting of 10 mmol L⁻¹ HCl + 11 mmol L⁻¹ imidazole, 0.15% (w/v) hydroxyethylcellulose, pH 6.0 (leading electrolyte) and 5 mmol L⁻¹ benzoic acid + 6 mmol L⁻¹ imidazole, pH 6.5 (terminating electrolyte). Separation was performed at a driving current of 80 μA and for detection current was decreased to 30 μA. Using contactless conductivity detection, the calibration curves in the tested concentration range up to 2.5 mmol L⁻¹ were linear for both metabisulfite and hydrosulfite complexes. The concentration detection limits for metabisulfite and hydrosulfite were 2.9 and 3.4 μmol L⁻¹, respectively. For 1 mmol L⁻¹ concentration, values of R.S.D. (n = 6) were 2.6% for hydrosulfite and 0.8% for metabisulfite. Isotachophoretic determination took about 20 min. The elaborated isotachophoretic procedure is simple to perform, sufficiently sensitive and accurate. In addition to this, low cost of analyses makes the method an alternative procedure to methods used so far for the determination of oxoanions of sulfur.